This invention relates to a process for producing mesocarbon microbeads of uniform particle size distribution by using as a starting material a heavy oil, that is, a heavy hydrocarbon oil originated from petroleum, coal, oil sand, oil shale or the like.
It is known in the prior art that mesocarbon microbeads (hereinafter referred to by the abbreviation "MC") can be obtained by heat treating a heavy oil at a temperature of 350.degree. to 500.degree. C. to obtain a heat-treated pitch and separating optically anisotropic microspheres (mesophase microspheres) formed within the pitch from the pitch matrix by solvent extraction. MC obtained in this manner are carbon precursors of spherical shapes close to perfect spheres of diameters of 1 to 100 microns and are constituted by condensed polycyclic aromatics in laminated alignment in a specific direction. Because of their unique form and crystalline structure, these MC have high electrical, magnetic, and chemical activities, and extensive utilization thereof in various diversified fields is expected.
More specifically, there are great expectations for the utilization of these MC for production of various industrial materials, examples of which are: special carbon materials such as high-density isotropic carbon materials and electrical resistance carbons prepared by carbonization after molding thereof; composite materials such as electroconductive ceramics, dispersion-reinforced metals, and electroconductive plastics prepared by carbonizing the MC as they are and thereafter blending the resulting material with other materials; and chemical materials such as catalyst supports and packing material for chromatography prepared by forming the MC into particles as they are or after carbonization.
For certain applications such as those for chromatography packing material and catalyst support among the above enumerated utilizations, the particle size of the MC is required to uniformly conform to specific sizes. However, the particle size of MC produced by a process depending on ordinary heat treatment of a heavy oil is distributed over a broad range (which may be as broad as 1 to 100 microns in most cases). Accordingly, the production of MC of narrow particle-size distribution by some method is desired in many fields. For fulfilling this need, some methods as described below are thought of or have been proposed.
(a) A method wherein a portion of specific particle sizes is separated out by sieving or by mechanical dispersion from MC produced by an ordinary process.
(b) A method wherein, by blowing superheated steam into a heavy oil thereby to agitate and heat the oil, thereby carrying out uniform heat treatment of the heavy oil, MC of narrow particle-size distribution are obtained (Japanese Pat. Publn. No.9599/1978).
(c) A method wherein the growth of the mesophase microspheres is suppressed by using one or more additives (as disclosed, for example, in "Tanso" ("Carbon"), No.77, P.61 (1974)).
However, none of these methods can be said to be completely satisfactory. More specifically, for example, it is difficult in the above method (a) to classify efficiently on an industrial scale the MC which are microspheres of micron size. In the methods (b) and (c), it becomes difficult to obtain MC of perfect spherical shape, and the effectiveness in uniformization of the particle size is still inadequate.